CDs (Compact Disk) and DVDs (Digital Versatile Disk) have respective unified physical format standards in which information is recorded into prepits at a linear velocity of 1.3 m/s for CDs and at a linear velocity of 3.49 m/s for DVDs regardless of whether the information is audio/video information or code information.
For apparatuses (CD players and DVD players) for reproducing audio/video information thus recorded on a disk at a constant linear velocity, conventionally, access performance is not considered to be important, and CLV (Constant Linear Velocity) control is performed in order to secure a low level of noise and vibration. In CLV control, the number of revolutions of a spindle motor is controlled in such a manner that a transfer rate (or linear velocity) is constant over a disk range from an inner circumference to an outer circumference of the disk. Such control is achieved as follows. The phase of the frequency of a reproduction clock in a PLL (Phase-Locked Loop) control section of a signal processing circuit is synchronized with the phase of the frequency of a reference clock obtained by frequency-dividing a quartz oscillator, and the frequency of the reproduction clock is controlled using the frequency of the frequency-divided reference clock, thereby generating a control signal for the spindle motor.
For apparatuses for reproducing a disk in which computer code information is recorded (a CD-ROM [Read-Only Memory] drive and a DVD-ROM drive), jitter-free for controlling the reproduction clock frequency per se of the PLL of the signal processing circuit is introduced, and CAV (Constant Angular Velocity) control is performed to obtain satisfactory fast-speed access performance. In CAV control, a spindle motor is controlled in such a manner that the number of revolutions is constant over a disk range from an inner circumference to an outer circumference of the disk.
Recently, hybrid disks which are CDs, DVDs, or the like in which audio or video information and computer code information are mixed have been produced. For such disks, conventionally, there is not a definition, a regulation, nor a proposal as to the order of pieces of information to be recorded, and a disk site at which information about the size of a unit of information will be recorded on the disk. For example, a considerably large size of code information may be recorded after a considerably short-time of music. Conversely, a considerably small size of code information may be recorded after a considerably long-time of music.
For such a disk, in the conventional art, audio/video information and code information are all reproduced by either a CLV control method or a CAV control method. Specifically, all information on the disk is subjected to data processing for audio/video information using CLV control where a transfer rate is reduced all over the disk. Alternatively, all information on the disk is subjected to data processing for code information (specifically, information, such as audio, is also temporarily stored in a cache memory or the like and thereafter transferred as memory information to the outside) using CAV control where a transfer rate is increased toward the outer circumference of the disk.
In the case where all information on a disk is reproduced using CLV control, code information is reproduced using CLV control even if code information is predominantly recorded on the disk. In such a case, even when code information is randomly accessed from an application on a host computer, the response time of a spindle motor predominantly occupies the access time, resulting in a significant reduction in access speed. Further, the noise caused by driving the motor in the access causes problems.
In the case where all information on a disk is reproduced using CAV control, random access seldom occurs since audio/video information is predominantly recorded. Although a host computer exhibits almost the same performance in outputting audio or displaying moving images if a transfer rate is greater than or equal to a predetermined value, a spindle motor is rotated at a higher speed greater than or equal to a required value, so that rotation, or vibration due to mass eccentricity or the like causes noise.
For a kind of CD (CD-EX (Extra) or the like), a reproduction apparatus capable of switching between CLV and CAV control is available, in which music information is subjected to CLV control, while code information, such as data relating to lyrics or songs, or artist information, is subjected to CAV control. Such a reproduction apparatus distinguishes audio information from code information using disk information recorded in a lead-in area, a TOC (Table Of Contents) area, and the like, or a sub-code defined in a logical format. Based on this identification, CAV control and CLV control are switched.
In the above-described technique in which CLV control and the CAV control are switched, when a disk is sequentially read from an inner circumference toward an outer circumference, a switching operation between CLV control and CAV control occurs every time the type of information is changed, resulting in a reduction in an average reproduction rate. Further, noise or heat is generated in a spindle motor in the switching.
The present invention is provided to solve the above-described problems. The object of the present invention is to provide: an information reproduction apparatus which appropriately selects CLV or CAV control, depending on information to be reproduced; an information carrier having an information recording area for recording information suitable for reproduction using CLV/CAV control; and an information recording apparatus for recording information on the information carrier.